Conventionally, there have been a method using Wi-Fi and a method using inaudible sound (ultrasonic sound) as indoor positioning methods.
A Wi-Fi positioning system includes Wi-Fi access points and user mobile terminals. In this system, a mobile terminal receives radio waves emanating from multiple access points to estimate the current location using access point-specific information (e.g., MAC address) and a radio field strength pattern. However, the accuracy of this system is relatively low, which is about 5 m to 10 m, and even using a technique called SLAM (Simultaneous Localization and Mapping), the accuracy can be improved only up to about 2.5 m. Further, it is necessary to make a field survey and create a radio map in advance in order to use this system. With the construction or abolition of an access point, the radio map needs updating, and this increases the cost for map creation and maintenance.
In contrast, the accuracy of the system using inaudible sound can be improved up to about 50 cm or 1 m. In addition, the system has the advantage of eliminating the need for the radio map. As an example of such a system, there is an indoor positioning system described in Patent Document 1 mentioned below. This positioning system includes a position beacon transmitting device and a position beacon receiving device.